In a novel marriage of conservation and modern biology, scientists have created stem cells from two endangered species, which could help ensure their survival.

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The drill - a close relative of the mandrill - is being squeezed by loss of habitat and hunting

The northern white rhino is one of the most endangered animals on Earth, while the drill - a west African monkey - is threatened by habitat loss and hunting.

The scientists report in Nature Methods that their stem cells could be made to turn into different types of body cell.

If they could turn into eggs and sperm, "test-tube babies" could be created.

Such applications are a long way off, but research team chief Jeanne Loring said she had been encouraged by the results on the rhino cells, which they had not really expected to be successful.

The stem cells were made from skin by a process of "re-programming", where retroviruses and other tools of modern cell biology are used to bring the cells back to an earlier stage of their development.

At this stage they are said to be "pluripotent", meaning they can be induced to form different kinds of specialised cell such as neurons and cartilage.

This kind of science entails a fair amount of trial and error, and the researchers expected it would work with the drill because there is lots of experience with primates - but the rhino was a different matter.

"It wasn't easy - we had to do a lot of fiddling to make it work, but it did work," Dr Loring told BBC News.

Along the test-tube

The initial application for this kind of technology might be medicinal.

If animals are suffering from degenerative diseases such as diabetes, stem cells could in principle be turned into replacements for cells that are ceasing to function.

Studies using this approach are underway in humans for health issues as different as heart failure, blindness, stroke and spinal injuries, though routine use is another matter.

But a more exciting idea is to create embryos by inducing the stem cells to make gametes - eggs and sperm.

"Making gametes from stem cells is not routine yet, but there are some reports of it being done with laboratory animals," said Dr Loring.

The rhino stem cells were shown to be capable of forming neurons (red)

Last month, a Japanese team reported turning mouse stem cells into sperm, which were then used to father mouse embryos.

Other research teams are looking to cloning to rescue seriously endangered species. But this team believes the creation of new embryos would be a better bet.

"Cloning has not worked well for endangered species - the frequency of success is very low," said Dr Loring.

"And here, you have the possibility to make new genetic combinations rather than cloning which simply reproduces existing animals."

Embryos created this way could potentially be raised in surrogate mothers from closely related species.

'Last-ditch effort'

Robert Lacy, a conservation scientist at the Chicago Zoological Society and chairman of the Conservation Breeding Specialist Group attached to the International Union for the Conservation of Nature (IUCN), said the technique might one day help to bring endangered species back from the brink, although lots more work remained to be done.

"The prospects for using these techniques for continuing the genetic lineages of the last few individuals of a species will be a last-ditch effort, after we have failed to protect the species in earlier, simpler, cheaper, and more effective ways," he said.

The northern white rhino is one of the world's most endangered species with only seven alive

"Only when numbers get so low that the genetic contribution of every last animal (including those represented only in frozen cell lines) contributes measurably to the total species diversity - maybe around 10 individuals - would we want to do everything possible to ensure that those genes are transmitted to future generations.

"Tragically, northern white rhinos have undergone just such a decimation."

The white rhinoceros is surviving well in southern Africa despite an increasing threat of poaching.

But with the northern sub-species (Ceratotherium simum cottoni), it is a very different story.

Three years ago, the wild population was down to just four individuals living in a national park in the Democratic Republic of Congo (DRC).

However, more recent expeditions have failed to locate even this tiny stock; and it is likely that the seven living in captivity are the only representatives left on the planet.

The drill (Mandrillus leucophaeus) - a less colourful cousin of the more familiar mandrill - is not in quite such a parlous state, but numbers in its native habitat in Cameroon and Nigeria are declining, mainly due to hunting, and the species carries an Endangered rating.

The stem cell research brings together conservation scientists with those involved in cutting-edge laboratory work, including Jeanne Loring who, as a world-renowned stem cell researcher, heads the Center for Regenerative Medicine at the Scripps Research Institute in La Jolla, California.

Their immediate aim is to replicate their rhino work with 10 other endangered animals. She would not be drawn on what they all are, but an elephant is among them.